Electroacoustic transducer construction suitable for operation in deep water



Aug. 3, 1965 F. MASSA 3,199,071 ELECTROACOUSTIC TRANSDUCER CONSTRUCTIONSUITABLE FOR OPERATION IN DEEP WATER Filed April 20. 1961 ATTORNEYS.

United States Patent F 3,199,071 ELECTRGACGUSTIQ TRANEDUCER CONSTRUGTKQN SUITABLE EUR fiPERATEON EN DEER? WATER Frank Massa, Cohasset, llorfolh, Mass, assignor, by rncsne assignments, to Dynamics (lorporationof America, New York, N.Y., a corporation of New York Filed Apr. 20,1961, Ser. No. 104,42ti 16 Claims. (Cl. 346-) This invention relatesgenerally to underwater sound transducers and more particularly to newand improved electro-acoustic transducers adapted for the conversion ofelectrical energy to acoustic energy and also for the converison ofacoustic energy to electrical energy;

It is well known in the art that an efficient electroacoustic transducermay be designed by employing piezoelectric materials for the conversionof electrical signals to mechanical vibrations. A conventional design ofsuch a transducer makes use of an assembly of piezoelectric expanderplates, cut from ammonium dihydrogen phosphate or some other suitablepiezoelectric material, which are operated at their natural resonantfrequency as illustrated, for example, in U.S. Patent 2,521,642 Such adesign is limited to relatively high frequency efiicient operationbecause the natural frequency of typical prior art crystal plateassemblies usually falls in the frequency range above 15,000 cycles persecond. For lower frequencies, the plates of these prior artarrangements become impractically long in their dimensions and aresubject to easy fracture when their assembly is attempted.

Accordingly, it is a general object of this invention to improve theconstruction of underwater transducers, and especially transducersoperating at frequencies generally in the region below approximately15,000 cycles per second.

Another object of this invention is to provide a new and highlyefiicient transducer construction which is pres sure equalized so thatsatisfactory operation can be achieved at great submerged depths underwater.

It is still another object of this invention to provide a transducer ofan etficient size wherein the radiating surface occupies a large portionof the housing dimensions.

It is another object of the invention to provide a transducer unit thatmay be conveniently assembled in multiple arrays whereby a very largeradiating surface may be achieved with low manufacturing cost.

Other objects of the invention will become obvious to those skilled inthe art from the following description in which the novel features whichcharacterize the invention are set forth with particularity in theappended claims. The invention, itself, however, both as to itsorganization and method of operation, as well as advantages thereof,will best be understood from the following description of severalembodiments thereof taken in conjunction with the accompanying drawingswherein:

FIGURE 1 is an end View showing the radiating surface of a newtransducer embodying the invention;

FIGURE 2 is an elevational View, partially in cross section, of a newtransducer taken along the line 22 of FIGURE 1;

FIGURE 3 is a partial sectional view, similar to FIG- URE 2, showinganother illustrative embodiment of active transducer element adapted foruse in the transducer assembly of the present invention;

FIGURE 4 is a perspective view of one of the crystal plates used in theembodiment of FIGURE 2 and arsaan Patented Aug. 3, 1965 FIGURE 5 is aperspective view of a split polarized ceramic cylinder which may be usedas an alternative construction to the illustrative embodiment of FIGURE3.

Referring now to the drawings, and more particularly to EGURE 1 thereof,the reference numeral 10 identifies the radiating plane surface of atransducer assembly 12. Although the radiating surface 10 is shown as asquare, it will be appreciated that any other configuration, such as acircle or a polygon could be used.

Referring now to FIGURE 2, the transducer assembly 12 is shown ascomprising a vibratile plate member 14 mounted within the frame-likeportion 16 of the housing structure and flexibly attached to the housingstructure by the molded rubber member 13. The rubber member 18 also ismolded over the front radiating surface of the vibratile plate member 14to provide a protective surface 2% for permitting improved long-lifeperformance under water.

Advantageously, a cylindrical housing member 22 is secured as by brazingor any other suitable means, to the frame-like portion 16 to provide acompletely sealed 7 housing to enclose the active transducer assembly.In accordance with a feature of this invention, the unique transducerstructure comprises the vibratile plate member 14 and an assembly ofpiezoelectric crystal plates 24, such as 45 Z-cut ammonium dihydrogenphosphate, or 45 X-cut rochelle salt, or any other piezoelectriccrystals which may be set into vibration by the application of analternat ing voltage to a set of electrodes 26. The crytsal plateassembly is firmly bonded to a prepared flat face 84 of the Vibratileplate member 14, and to a similarly prepared flat surface 86 of a weight28 as shown in FIGURE 2. A thin insulating Bakelite sheet (not shown)may be interposed and securely bonded between the ends of the crystalplates 24 and the surfaces of the adjoining plate 14 j and weight 28, ifdesired.

The purpose of providing the weight member 28 to load the crystalstructure is to resonate the vibrating crystals at a lower frequencythan would be possible were the loading weight omitted. In order thatthe crystal vibration amplitude may be held at a minimum with thecorresponding advantageous reduction in stress, it is advantageous tomake the vibratile plate 14 as light as possible, While making most ofthe load for frequency reduction reside in the non-radiating weightmember 28. The vibratile plate 14 therefor, in one illustrativeembodiment, is made of aluminum and, in cases where still further weightreduction is desired, the aluminum may be cast as a porous sponge-likemass which will preserve the rigidity of the plate, which is essentialfor satisfactory radiation of sound under water. The vibratile plate 14illustratedin FIGURE 2 is shown as a porous spongelike aluminum masshaving inclusions of gas pockets 88 dispersed through its volume wherebyits density is reduced.

The magnitude of the weight 23 is adjusted to result in a combinedresonant frequency of the crystal plates 24, and the masses of the plate14 and Weight 28 as desired for the operating frequency of thetransducer. Advan tageously a flexible spider member 343 is securelyfastened to the center of the weight 28 as by the threaded fastener andspacer 34, and is also secured at its periphery to a ring member 36,which, in turn, is secured by any suitable means, such as brazing orwelding, to the inner periphery of the housing structure 22. Inaccordance with the invention, the spider member 3% has transverserigidity and keeps the weight 23 from being sheared off as at the bondedcrystal surface during shock and vibration ml? "the transducer.

An end cap 38 is fastened to the housing 22, as by means of the radiallydispose-d screws 4%. Advantageously an O-ring 42 provides a seal betweenend cap 38 and housing 22, as shown. Insulated terminals 44 are providedto permit transfer of the electrical connections from the electrodes 26of the crystal plates 24 to the external cable 46'. A cable glandhousing 43 is fastened .to the end cap 38 as by means of the screws 50and and O-ring 52 provides the necesary underwater seal. The cable 46 issealed by the assembly of the compression rubber gland 54, the washer 56and the nut 58. Those .skilled in the art will appreciate that nut 58 istightened sufliciently to provide compression of the gland 54 to thesurface of the cable In order to pressure equalize the assembly so thatthe structure will not be damaged due to the higher static pressuredeveloped in deep water, it is a feature of this invention to provide aflexible rubber sleeve 6t? which is :sealed to opposite ends of thecylindrical housing 22, as

by means of the metallic bands 62. or other suitable means. An orifice64 is formed through the wall of the housing 22, as shown, to providecommunication between the inner enclosure of the housing 22 and thereservoir enclosure 66 defined by the sealed rubber sleeve so and theouter surface of housing 22. A suitable fluid, such as castor oil, fillsthe inner enclosure of the trans :ducer assembly and the reservoirenclosure 66 of the as- :sembly. The oil may be poured into thetransducer before the attachment of the end cap 38, and the rubbersleeve tit) may be pulled out from the housing as by means of a vacuum,to allow the oil to run into the formed reservoir enclosure 66.

In accordance with a further feature of this invention, :a low acousticimpedance member 68, such as cork, is placed inside the transducerstructure. The members 68 serve as a pressure release during thevibration of the plate 14 during operation of the transducer andprevents other words, the compression of the air cells prevents thepressure from being built up in the fluid, and there- "fore, serves as apressure release.

The above description of the new low frequency transducer contemplatesthe use of piezoelectric crystals forming the vibrating transducermaterial. An illustrative detailed showing of a 45 Z-cut ammoniumdi-hydrogen' phosphate crystal which is suitable for use in the inven-'-tion is shown in FIGURE 4 of the drawing. A pair of metaltic electrodesurfaces 26 are cemented to the opposite faces of the crystal plate 24as shown. When potential surface.

crystal structure. The electrical conducting leads 70' and 72' connectthe polarized ceramic cylinder 74 to the terminals of a suitable powercable so that electrical operating power may be supplied to thetransducer.

In accordance with another feature of this invention, it has been foundadvantageous to split the outer cylindrical electrode into two separatesemi-cylindrical haif electrodes 7 8 and 89 as illustratively shown inFIGURE 5; In polarizing the ceramic cylinder, the D.-C. polarizingpotential is applied between the half electrodes 73 and St), and acenter tap from the polarizing potential is connected to the innercontinuous cylinder electrode 82. By this polarizing arrangement, thetwo A.-C. connections will remain on the external surfaces 78 and 89 ofthe ceramic cylinder and thereby increase the convenience of theassembly. It will be appreciated by those skilled in the art that it is,of course, equally possible to polarize the'cer'amic cylinder in aconventional manner usmg a continuous outer cylindrical electrode forone potential surface and the inner cylindrical electrode for the secondThe inner electrode connecting wire would then be passed through a holethat would be provided through the loading weight 28 in order to permitelectrical connection to be established between the inner surface of thecylinder andthe terminals 44.

While there has been shown and described several specific embodiments ofthe present invention, it will of course, be understood that variousmodifications and alternative constructions may be made withoutdeparting from the true spirit and scope of the invention. Therefore, itis intended by the appended claims to cover all such modifications andalternative constructions as fall alternating potentials are applied tothe electrodes 26, i

the crystal plate will vibrate correspondingly in a manner well known inthe art. Advantageously, a plurality of crystal plates 24, as shown inFIGURE 2, may be provided with all the positive polarities connectedtogether as shown. Suitable electrical conducting leads '70 and '72conect the crystal plate electrodes 26 to the terminals 44 so thatelectrical operating power may be supplied to the transducer, throughthe cable 46.

As an alternate transducer material which may be utilized in theinvention, the crystals of FIGURE 2 may be replaced by other materials,as for example, a stack of magnetostrictive elements or by a polarizedpolycrystaline ceramic such as barium titanate or lead zirconate asillustrated in FIGURE 3. As shown in FIG URE 3, the crystal plates 24 ofFIGURE 2 have been replaced by the polarized ceramic cylinder 74. Theloaded ceramic cylinder '74 will operate at reduced resonant frequencyfor the same reason described above with the within their true spiritand scope.

What is claimed as the invention is: w l. The improvement of anelectroacoustic transducer assemblyfo'r generatin underwater soundcomprising the combination of electromechanical transducer means hav*ing first and second plane surfaces spaced from each other and capableof being set into vibration by the appli= cation of an alternatingcurrent to sai-d transducer means a fixed housing structure defining anenclosure for said transducer means, a vibratile plate flexibly mountedt6 said housing structure, and secured to said first plane surface ofsaid transducer means, a solid weight member having a plane surfacesecured to said second plane surface of said transducer means, flexiblesuspension means for supporting said solid Weight member in said housingstructure, a flexible chamber member defining an exteriorly sealedcompartment, said exteriorly sealed compartment being in internal fluidcommunication with the enclosure of said housing structure through apassageway formed in said housing structure, a fluid disposed within theenclosure of said housing structure and within said exteriorly sealedcompartment, said fluid being capable of easily flowing between theenclosure of said housing structure and the exteriorly sealedcompartment, and electrical terminal means on said housing structure forconnecting external electrical power to said transducer means.

2. The improvement of an electroacoustic transducer assembly forgenerating underwater sound comprising the combination ofelectromechanical transducer means capable of being set into vibrationby the application of an alternating current, a fixed housing structuredefining an enclosure for said transducer means, a vibratile platefiexlbly mounted to said housing structure and secured to saidtransducer means, a solid weight member attached to saidelectromechanical transducer means, flexible suspension means forsupporting said solid weight member from said housing structure, aflexible chamber member defining an exteriorly sealed compartment, saidexteriorly sealed compartment being in fluid communication with theenclosure of said housing structure through a passageway formed in saidhousing structure, a fluid disposed within the enclosure of said housingstructure and within .5 I/ said exteriorly sealed compartment, saidfluid being capable of easily flowing between the enclosure of saidhousing structure and the sealed compartment through sa1d passageway,and electrical terminal means on said housing structure for connectingexternal electrical power to said transducer means.

3. The improvement of an electroacoustic transducer assembly forgenerating underwater sound comprising the combination ofelectromechanical transducer means capable of being set into vibrationby the application of an alternating current, a fixed housing structuredefining an enclosure for said transducer means, a vibratile plateflexibly mounted to said housing structure and secured to saidtransducer means, said vibratile plate being formed with cellularinclusions of gas to reduce the density of said plate, a solid weightmember attached to said electromechanical transducer means, flexiblesuspension means supporting said solid member from said housingstructure, a flexible chamber member defining an exteriorly sealedcompartment, said sealed compartment being in fluid communication withthe enclosure of said housing structure through a passageway formed insaid housing structure, a fluid disposed within the enclosure of saidhousing structure and within said sealed compartment, said fluid beingcapable of easily flowing between the enclosure of said housingstructure and the sealed compartment through said passageway, andelectrical terminal means on said housing structure for connectingexternal electrical power to said transducer means.

4-. The improvement of an electroacoustic transducer assembly inaccordance with claim 3 wherein said housing structure and sealedenclosure are filled with a liquid.

5. The improvement of an electroacoustic transducer assembly forgenerating underwater sound comprising the combination ofelectromechanical transducer means having first and second spaced apartplane surfaces capable of being set into vibration by the application ofan alternating current, a fixed housing structure definingan enclosurefor said transducer means, a vibratile plate flexibly mounted to saidhousing structure and attached to said first plane surface of saidtransducer means, a solid weight member having a plane surface attachedto said second plane surface of said electromechanical transducer means,flexible suspension means for supporting said solid weight member insaid housing structure, and electrical terminal means on said housingstructure for connecting external electrical power to said transducermeans. 7

6. The improvement of an electroacoustic transducer assembly inaccordance with claim wherein said vibratile plate is formed withcellular inclusions of gas to reduce the density of said plate.

7. The improvement of an electroacoustic transducer assembly inaccordance with claim 5 wherein one face of said vibratile plate isexposed to the exterior of said housing structure and further comprisinga flexible water impervious material covering the exposed face of saidvibratile plate.

8. The improvement of an electroacoustic transducer assembly forgenerating underwater sound comprising the combination ofelectromechanical transducer means formed of a plurality of stackedpiezoelectric plates capable of being set into vibration by theapplication of an alternating current, a fixed housing structuredefining an enclosure for said transducer means, a vibratile plateflexibly mounted in said housing structure and attached to saidtransducer means, a weight member attached to said electromechanicaltransducer means, flexible suspension means for supporting said weightmember from said housing structure, a flexible chamber member definingan exteriorly sealed compartment, said sealed compartment being in fluidcommunication with the enclosure of said housing structure through apassageway formed in said housing structure, a fluid disposed within theenclosure of said housing structure and within said sealed compartment,said fluid being capable of easily flowing between the enclosure of saidhousing structure and the sealed compartment through the passageway andelectrical terminal means on said housing structure for connectingexternal electrical power to said transducer means.

9. The improvement of an electroacoustic transducer assembly forgenerating underwater sound comprising the combination ofelectromechanical transducer means formed of polarized ceramic materialcapable of being set into vibration by the application of an alternatingcurrent, a fixed housing structure defining an enclosure for saidtransducer means, a vibratile plate flexibly mounted to said housingstructure and attached to said transducer means, a weight member securedto said electromechanical transducer means, flexible suspension meansfor supporting said weight member from said housing structure, aflexible chamber member defining a sealed compartment, said sealedcompartment being in fluid communication with the enclosure of saidhousing structure through a passageway formed in said housing structure,a fluid disposed within the enclosure of said housing structure andwithin said sealed compartment, said fluid being capable of easilyflowing between the enclosure of said housing structure and the sealedcompartment through said passageway and electrical terminal means onsaid housing structure for connecting external electrical power to saidtransducer means.

it). The improvement of an electroacoustic transducer assembly inaccordance with claim 9 wherein said polarized ceramic material is inthe form of a polarized ceramic cylinder having first and second planesurfaces respectively at opposite ends or" the cylinder, said firstplane surface being attached to said vibratile plate and said secondplane surface being attached to said solid weight member.

11. The improvement of an electroacoustic transducer assembly inaccordance with ciaim 10 wherein said polarized ceramic cylinder isprovided with at least two electrically separated metallic electrodes.

12. The improvement of an electroacoustic transducer assembly forgenerating underwater sound comprising the combination or"electromechanical transducer means having a pair of parallel planesurfaces capable of being set into vibration by the application of analternating current, a fixed housing structure defining an enclosure forsaid transducer means, a vibratile plate flexibly mounted in saidhousing structure and attached to one of said parallel plane surfaces ofsaid transducer means, a weight member secured to the other parallelplane surface of said electromechanical transducer means, flexiblesuspension means for supporting said weight member from said housingmeans, a flexible chamber member defining a compartment, saidcompartment being in fluid communication with the enclosure of saidhousing structure, -a fluid disposed within the enclosure of saidhousing means and within said compartment, said fluid being capable ofeasily flowing between the enclosure of said housing structure and thecompartment.

13. The improvement of an electroacoustic transducer assembly inaccordance with claim 12 characterized in that said weight member is ofgreater mass than said vibratile plate.

14. The improvement of an electroacoustic transducer assembly forgenerating underwater sound comprising the combination ofelectromechanical transducer means having first and second,spaced-apart, parallel plane surfaces, electrical conductor meansconnected to said transducer means for applying an alternating currentto set the transducer means into vibration, a housing structure definingan enclosure for said transducer means, a vibratile plate flexiblymounted in said housing structure and attached to said first parallelplane surface of said electromechanical transducer means and a weightmember secured to said second parallel plane surface of saidelectromechanical transducer means.

7 8' 15. The improvement of an electroacoustic transducer tromechanicaltransducer means is maintained under a assemblyin accordance with claim14 wherein the mass static pressure bias between said vibratile plateand said of said weight member is greater than the mass of said weightmember.

vibratile plate. No references cited.

16. The improvement of an electroacoustic transducer 5 assembly inaccordance with claim 14 wherein said elec- CHESTER L- JUSTUS, PrimaryExaminer.

1. THE IMPROVEMENT OF AN ELECTROACOUSTIC TRANSDUCER ASSEMBLY FORGENERATING UNDERWATER SOUND COMPRISING THE COMBINATION OFELECTROMECHANICAL TRANSDUCER MEANS HAVING FIRST AND SECOND PLANESURFACES SPACED FROM EACH OTHER AND CAPABLE OF BEING SET INTO VIBRATIONBY THE APPLICATION OF AN ALTERNATING CURRENT TO SAID TRANSDUCER MEANS, AFIXED HOUSING STRUCTURE DEFINING AN ENCLOSURE FOR SAID TRANSDUCER MEANS,A VIBRATILE PLATE FLEXIBLY MOUNTED TO SAID HOUSING STRUCTURE, ANDSECURED TO SAID FIRST PLANE SURFACE OF SAID TRANSDUCER MEANS, A SOLIDWEIGHT MEMBER HAVING A PLANE SURFACE SECURED TO SAID SECOND PLANESURFACE OF SAID TRANSDUCER MEANS, FLEXIBLE SUSPENSION MEANS FORSUPPORTING SAID SOLID WEIGHT MEMBER IN SAID HOUSING STRUCTURE, AFLEXIBLE CHAMBER MEMBER DEFINING AN EXTERIORLY SEALED COMPARTMENT, SAIDEXTERIORLY SEALED COMPARTMENT BEING IN INTERNAL FLUID COMMUNICATION WITHTHE ENCLOSURE OF SAID HOUSING STRUCTURE THROUGH A PASSAGEWAY FORMED INSAID HOUSING STRUCTURE, A FLUID DISPOSED WITHIN THE ENCLOSURE OF SAIDHOUSING STRUCTURE AND WITHIN SAID EXTERIORLY SEALED COMPARTMENT, SAIDFLUID BEING CAPABLE OF EASILY FLOWING BETWEEN THE ENCLOSURE OF SAIDHOUSING STRUCTURE AND THE EXTERIOLY SEALED COMPARTMENT, AND ELECTRICALTERMINAL MEANS ON SAID HOUSING STRUCTURE FOR CONNECTING EXTERNALELECTRICAL POWER TO SAID TRANSDUCER MEANS.